This research program has been designed to discover the factors that determine human listeners' capabilities to extract information from auditory patterns. Previous work has concentrated on listeners' abilities to resolve the frequency, duration, and intensity of temporal components of work-length, tonal sequences. These studies have demonstrated major effects of stimulus uncertainty, especially that imposed by variation in the context in which test tones occur. In the proposed work we will search for those contextual features which contribute most heavily to this uncertainty effect. Our work has also shown that the time course of auditory perceptual learning is significantly longer for discriminations of elements within word-length sequences than would have been predicted from studies using simpler stimuli, for example tones in a quiet or noise background. We will continue to map this time course for discriminations made under various levels of stimulus uncertainty and for several psychophysical procedures, in particular the method-of-adjustment, same different, and three-allernative forced-choice methods. We will also attempt to determine those characteristics of a stimulus catalog an observer learns in addition to those which must be used in a primary discrimination or detection task.